This invention relates generally to a quartz crystal oscillator of the type used in electronic wristwatches and more particularly to a quartz crystal oscillator package which has high strength, high internal vacuum, a good hermetic seal, and a low, flat profile. In conventional oscillator packages at least one flat face of the package is transparent to permit passage of a laser beam used in adjusting the frequency of the enclosed vibrator. The housing elements used to form the package are fabricated by etching a sheet of planar material such as quartz or glass. In the prior art the material was etched from both sides simultaneously to produce completed housing elements. This simultaneous etching method presents a problem in that the peripheral edges are a weak point leading to breakage of the package. Also in the prior art, the concave portion in which the crystal vibrator is enclosed in the completed package, is also etched while the peripheral edges are being formed by etching. As a result, the wall thickness of the package is reduced to approximately half the thickness of the original material leaving a wall which is structurally weak and subject to breakage.
An additional problem with the oscillator packages of the prior art is caused by the method of sealing the housing elements to the quartz crystal vibrator leaf. In the prior art, a low melting point solder has been used at the peripheral edges to provide the seal. However, outgassing from the solder at the time of sealing causes gas to enter the cavity wherein the vibrator leaf is enclosed. Thus, although the process is carried out under vacuum, the resulting product has a poor internal vacuum and produces an oscillator lacking in high Q performance. Because of the ultraminiature size of the completed oscillator package, even a small amount of inleakage of gas from the sealing material destroys the vacuum within the package.
What is needed is a quartz crystal oscillator package which has sufficient wall thickness to provide high strength and yet has a low profile. The peripheral edges of the package should not be a source of weakness and the sealing process should produce a high quality hermetic seal which does not permit gases to enter the enclosed volume of the package during the process of sealing.